全文获取类型
收费全文 | 20222篇 |
免费 | 1379篇 |
国内免费 | 42篇 |
学科分类
工业技术 | 21643篇 |
出版年
2024年 | 45篇 |
2023年 | 186篇 |
2022年 | 676篇 |
2021年 | 895篇 |
2020年 | 560篇 |
2019年 | 642篇 |
2018年 | 810篇 |
2017年 | 807篇 |
2016年 | 880篇 |
2015年 | 680篇 |
2014年 | 1000篇 |
2013年 | 1712篇 |
2012年 | 1366篇 |
2011年 | 1427篇 |
2010年 | 1103篇 |
2009年 | 1060篇 |
2008年 | 900篇 |
2007年 | 770篇 |
2006年 | 592篇 |
2005年 | 487篇 |
2004年 | 443篇 |
2003年 | 457篇 |
2002年 | 363篇 |
2001年 | 266篇 |
2000年 | 226篇 |
1999年 | 234篇 |
1998年 | 755篇 |
1997年 | 498篇 |
1996年 | 339篇 |
1995年 | 211篇 |
1994年 | 185篇 |
1993年 | 144篇 |
1992年 | 76篇 |
1991年 | 47篇 |
1990年 | 53篇 |
1989年 | 52篇 |
1988年 | 61篇 |
1987年 | 54篇 |
1986年 | 34篇 |
1985年 | 60篇 |
1984年 | 56篇 |
1983年 | 55篇 |
1982年 | 44篇 |
1981年 | 40篇 |
1980年 | 51篇 |
1979年 | 33篇 |
1978年 | 21篇 |
1977年 | 37篇 |
1976年 | 59篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
The first Brazilian uranium mine and mill are located on the Poços de Caldas plateau, in the Central State of Minas Gerais. The pre-operational environmental survey was carried out over a period of two years by the Brazilian Nuclear Energy Commission (CNEN), through the Instituto de Radioproteção e Dosimetria (IRD). The selection of the materials to be monitored, the sampling points and the radionuclides to be analysed were based on critical parameters taking into account the meteorological and hydrological characteristics of the site as well as land use. The results obtained are sufficient to characterize the environmental background of the area, and will allow an assessment of the environmental impact due to the operation of the facility and an evaluation of the adequacy of the effluent emmission control measures. In relation to their contribution to the population dose, the results indicated that 226Ra and 210Pb will be the important radionuclides. 相似文献
62.
We describe a patient with aspergillosis of the maxillary antrum, and systemic affectation (anemia, anorexia, fever). Through a Caldwell-Luck approach, the maxillary antrum was opened and an irregular mass removed, postoperatively the patient has done well, disappearing in two months the ORL and systemic symptoms. 相似文献
63.
64.
The preparation of p-type amorphous- or microcrystalline silicon often requires the use of a gas mixture containing diborane. Whereas the concentration of this gas in the process chamber is critical for the determination of the doping level, and thus of the properties, of resulting films, it is in practice very difficult to have a proper control of such a concentration owing to the degradation of diborane in the cylinder by polymerisation. The main consequence is a significant lack of reproducibility of results. The present paper analyses the problem and its practical influence, describes a simple diborane-degradation model, proposes certain approaches based thereon and shows experimental results illustrating the validity of the procedures suggested. It is finally concluded that the application of this simple model is a straightforward and effective way to control diborane doping level in p-type amorphous- or microcrystalline silicon. 相似文献
65.
66.
Luengo M. A.; Carrillo-de-la-Pe?a M. T.; Otero J. M.; Romero E. 《Canadian Metallurgical Quarterly》1994,66(3):542
Analyzes the relationships between impulsivity and antisocial behavior in a noninstitutionalized sample, taking into account the multidimensional nature of impulsivity and the diversity of types of antisocial behavior. Data were obtained in 1989 and 1990 from 1,226 adolescents aged 12–18 yrs as part of a longitudinal study of risk factors for drug abuse and delinquency. The patterns of stability or change of the various dimensions of antisocial behavior (rule breaking, vandalism, theft, aggression, and drug taking) in relation to impulsivity were investigated. The results support that self-report measures of impulsivity are closely correlated with antisocial behavior among adolescents. The longitudinally-oriented analysis of this work also shows that impulsivity is associated with a future increase in antisocial behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
67.
D. E. Wetzler P. F. Aramendía M. L. Japas R. Fernández-Prini 《International Journal of Thermophysics》1998,19(1):27-42
Thermal diffusivities of supercritical CO2 and C2H6 were determined over a wide density range with a photothermal technique. The thermal lens, formed by the degradation of the absorbed light energy as heat by the sample, allows the employment of a nonequilibrium method in the critical region. Controlling the refractive-index gradient, i.e., a density gradient, perturbations can be maintained at levels where convection is negligible. An easy-to-operate setup allowed us to measure thermal diffusivities in the density ranges 5 to 20 mol·dm–3 for CO2 at 308 and 313 K and 2 to 12 mol·dm–3 for C2H6 at 308 K with a standard precision of 15%. 相似文献
68.
Lopez Frederick G.; Fons-Scheyd Alia; Morúa Wendy; Chaliman Rebecca 《Canadian Metallurgical Quarterly》2006,53(4):543
This study examined the nature and impact of dyadic perfectionism over a 3-month interval within a sample of 116 college students who were currently involved in an intimate heterosexual relationship. Dyadic perfectionism scores were stable and correlated as expected with scores on concurrent measures of adult attachment orientations and relationship satisfaction. Logistic regression analyses revealed that, controlling for initial commitment status and adult attachment orientations, Time 1 dyadic perfectionism scores significantly and uniquely predicted relationship continuity 3 months later. Lastly, controlling for social desirability, relationship commitment status, and Time 1 adult attachment orientation scores, Time 1 dyadic perfectionism scores also uniquely predicted Time 2 relationship distress. Findings provide additional evidence that dyadic perfectionism is a risk factor for relationship dysfunction. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
69.
Preparation and characterisation of vanadium catalysts supported over alumina-pillared clays 总被引:1,自引:0,他引:1
M. A. Vicente C. Belver R. Trujillano M. A. Baares-Muoz V. Rives S. A. Korili A. Gil L. M. Gandía J. -F. Lambert 《Catalysis Today》2003,78(1-4):181-190
Supported vanadium-containing catalysts were prepared by impregnation of Al-pillared clays with NaVO3 precursor aqueous solutions. A montmorillonite and a saponite, both natural as well as previously pillared with Al13-Keggin polycations, were used as supports, being impregnated with solutions of the precursor by means of the incipient wetness technique. The layered structure of the supports is maintained after impregnation, and even after calcination of the impregnated solids at 500 °C, although with a significant worsening of the textural properties of the solids, in particular, a loss of specific surface area. Three crystalline vanadium-containing phases were identified in the impregnated solids, namely, NaV3O8, AlVO4 and V2O5 (shcherbinaite). The reduction of these phases to V3+ species was observed as wide processes in the 450–750 °C range, all of them centred at ca. 600 °C. 相似文献
70.
Lime mortars are often used for repairs to historic buildings. This paper investigates two forms of lime binder: fat and feebly-hydraulic,
in order to predict their long-term behaviours and hence ascertain which of the two possesses greater durability, so that
they may be used more efficiently in restoration. Mortars were tested for properties governing moisture movement and also
subject to durability cycles. The resistance to damage under freezing conditions was evaluated with the saturation coefficient.
Thermal cycles had no effect on the mortars and gave no indication of the relative durabilities of the binders. Salt crystallization
cycles, though effective in distinguishing the more durable of the two, were too aggressive to gauge a clear profile of salt
weathering and succeeded in rapidly decomposing the samples. Tests on the properties governing moisture movement produced
good indications of the degree to which the mortars permit flow through their fabrics. According to the results obtained,
fat lime mortars are more durable than those made with feebly-hydraulic lime. The results also suggest that the feebly-hydraulic
lime mortars are at a higher risk of decomposition by granular disintegration whereas fat lime mortars are better suited to
damp, slightly exposed conditions. These results disagree with the general opinion that hydraulic limes are more durable than
fat limes due to the additional strength and water insolubility arising from their hydraulicity. 相似文献